UNC-CH Department of Cell and Molecular Physiology

Migration and Cytoskeleton Remodeling in Vascular Smooth Muscle and Cancer Cells

The actin cytoskeleton participates in many fundamental processes including the regulation of cell shape, motility, and adhesion. Cell motility is dependent on the dynamic remodeling of the actin cytoskeleton, a process that is reliant on actin binding proteins that organize actin filaments into functionally specialized arrays. The Otey lab has recently identified a novel protein named palladin that is critically important for the maintenance of an organized actin cytoskeleton. Palladin is a molecular scaffold that participates in cytoskeletal organization by complexing with actin-associated proteins that regulate actin filament growth and bundling. The focus of my research is to explore the role of palladin in the following systems:

1- Cancer Metastasis

The actin cytoskeleton provides the basis for all forms of cell motility, including the pathological, invasive motility that is characteristic of metastatic cancer cells. Multiple studies have suggested that abnormal upregulation of palladin may contribute to the pathological, invasive motility of metastatic cancer cells. Thus, it is likely that aberrantly high levels of palladin protein may play a critical role in the pathological increase in cell motility that contributes to the spread of cancer by metastasis. Additional evidence for palladin’s role in invasive cancer comes from the identification of a mutation in the human palladin gene that is implicated in a rare form of inherited pancreatic cancer. Palladin levels are also upregulated in the sporadic (non-familial) form of pancreatic cancer, thus strongly implicating palladin as being an important player in this highly invasive disease. Together, these results point to the importance of understanding palladin’s function in invasive cancer cells, so we will test the hypothesis that high levels of palladin expression are required for invasion and metastasis of cancer cells.

The localized accumulation of vascular smooth muscle cells plays an important role in two major human pathologies: the development of atherosclerotic plaques and the restenosis that frequently occurs after balloon angioplasty. In both processes, smooth muscle cells undergo directed migration in response to growth factors. This migratory response can be modeled in tissue culture using the vascular smooth muscle cell line A7r5, which exhibits a similar migratory response when treated with platelet-derived growth factor (PDGF). In vascular smooth muscle cells, as in other cell types, the mechanisms that guide and control cell motility are not fully understood, but it is clear that the actin cytoskeleton plays an essential role. We have identified Eps8 as a novel binding partner for palladin. Eps8 is an actin-binding protein that links growth factor stimulation to actin dynamics via activation of the small GTPase, Rac. Our results suggest that palladin may participate in an Eps8-dependent pathway that connects growth factor stimulation to actin cytoskeletal function during cell migration. Thus, the focus of my work is to characterize the interaction between Eps8 and palladin, and to explore the role of these two proteins in the response of vascular smooth muscle cells to PDGF stimulation. These studies will test the hypothesis that (1) Eps8 recruits palladin to specific subcellular sites, in response to stimulation by PDGF, and (2) palladin promotes the formation of actin-rich structures involved in cell motility, so that (3) palladin plays an essential role in growth-factor mediated movement of vascular smooth muscle cells.

Goicoechea SM, Arneman D, Otey CA. (2008) Palladin’s Role in Actin Organization and Cell Motility. European Journal of Cell Biology. In Press.

Goicoechea S, Arneman D, Disanza A, Garcia-Mata R, Scita G, Otey CA. (2006) Palladin binds to Eps8 and enhances the formation of dorsal ruffles and podosomes in vascular smooth muscle cells. J Cell Sci. 119(Pt 16):3316-24.

Orr AW, Pedraza CE, Pallero MA, Elzie CA, Goicoechea S, Strickland DK, Murphy-Ullrich JE. (2003) Low density lipoprotein receptor-related protein is a calreticulin co-receptor that signals focal adhesion disassembly. J Cell Biol. 161(6):1179-89.

Goicoechea SM and JE Murphy-Ullrich. (2002) Cell surface calreticulin-thrombospondin de-adhesive activity in Calreticulin in Health and Disease. In P. Eggleton, M. Michalak (Eds.), Calreticulin. Georgetown, Texas: Landes Bioscience. 2nd Edition.

Goicoechea SM, Pallero MA, Eggleton P, Michalak M Murphy-Ullrich JE. (2002) Anti-adhesive Activity of Thrombospondin Is Mediated By The N-terminal Domain Of Cell Surface Calreticulin. J Biol Chem. 277 (40):37219-28.

Goicoechea SM, Tu Y, Hua Y, Chen K, Shen TL, Guan JL, Wu C. (2002) Nck-2 interacts with focal adhesion kinase and modulates cell motility. Int. J. Biochem. Cell Biol. 1255:1-15.

Goicoechea SM, Orr WA, Pallero MA, Eggleton P, Murphy-Ullrich JE. (2000) Thrombospondin mediates focal adhesion disassembly through interactions with cell surface calreticulin. J. Biol. Chem. 275(46):36358-68.

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